Amestris ROM is another OS based on the Android 4.1.2 Jelly Bean for the Galaxy S3 I9300. You can use this post and learn how to successfully flash this custom OS for your device in under 5 minutes without damaging the phone.

This is a guide for advanced Android users and, by installing the Amestris JB Custom ROM you will get multiple new custom features along with a dark theme named BlackDiamond which is an improvement from the stock theme used by TouchWiz of SGS3. Below you can find all the other main features of this custom ROM:

multi-language support added.

rooted, odexed all stock applications and jar files, zipaligned

stock kernel has been left installed.

CRT on-off animation, Insecured, Torch via Home button when using the lockscreen.

Skip Tracks via vol.btn.

busybox and superuser installed.

init.d support added.

disabled scrollcache.

MediaScanner fix added.

No Bloatware.

Extended power menu options, Multi CSC, Ametris OTA Updates button can be found in Settings menu.

The battery power charging level should be over 50% so that the phone won’t switch off in the middle of the updating process.

Don’t blame us in case something goes wrong and you lose data or you brick the phone in the process.

Ask for extra help in comments in case you cannot complete the custom ROM installation.

These were all the preparation steps that you had to go over before continuing to the ‘how-to’ tutorial guide. If you hit any roadblocks or you can’t seem to understand what all the steps are asking you to do, then you can leave a detailed comment at the end of this post and we will try to offer you a viable solution and help you flash all the custom OS files.

Download the Ametris ROM from HERE. Save the file on your PC and don’t unzip its contents.

Connect the SGS3 to your Computer and then move the Custom ROM zip on the phone’s internal SDcard. Disconnect the phone fromPC when the file is copied successfully. After that you can switch off the device.

Boot your phone into CWM Recovery by pressing simultaneously Volume Up, Home and Power. Release the buttons when the screen powers ON.

Next, select ‘backup and restore’ option and create a NANDROID backup of the currently installed ROM. After this restore point is created you can return to the main menu of the Recovery mode.

Select ‘wipe data/ factory reset’ option and confirm this process.

Select ‘install zip from sdcard’ now. This will help you flash the custom ROM zip.

Now you need to select ‘choose zip from sdcard’ file from the new Recovery menu. Find the ‘Ametris ROM’ zip file and confirm that you want to install it.

Return to the main menu of the CWM Recovery mode when the ROM is installed successfully.

Select ‘reboot system now’ and then wait until the phone boots into normal mode.

Enter your Google Account details and log into your device’s new custom ROM home screen.
Test all the functions of the Ametris Jelly Bean ROM and then tell us in comments which are your favorite features.

NOTE: If the first boot process of Ametris ROM doesn’t complete after 5 minutes have passed, or in case the SGS3 enters into a boot loop, then you will need to power it off completely. After that, you need to repeat the entire tutorial again and make sure that you don’t skip any instructions listed above.

Custom ROMs are usually acting up during the installation and you should retry to install them two / three times until the install is complete.

If you don’t like this new ROM, then you can restore the NANDROID backup of your previously installed ROM using the same Custom Recovery mode menu.

If you have any other questions, use the comments field below and we will offer you the correct replies you’re looking for and that should help you flash new custom ROMs from now on.